﻿using System.Reactive.Concurrency;
using System.Reactive.Disposables;
using System.Windows.Threading;
using TailBlazer.Domain.Infrastructure;

namespace TailBlazer.Infrastructure;

public class SchedulerProvider : ISchedulerProvider
{
    public IScheduler MainThread { get; }

    public IScheduler Background { get; } = TaskPoolScheduler.Default;

    public SchedulerProvider(Dispatcher dispatcher)
    {
        MainThread = new DispatcherScheduler(dispatcher);
    }

}


/// <summary>
/// Represents an object that schedules units of work on a <see cref="System.Windows.Threading.Dispatcher"/>.
/// </summary>
/// <remarks>
/// This scheduler type is typically used indirectly through the <see cref="Linq.DispatcherObservable.ObserveOnDispatcher{TSource}(IObservable{T})"/> and <see cref="Linq.DispatcherObservable.SubscribeOnDispatcher{TSource}(IObservable{TSource})"/> methods that use the Dispatcher on the calling thread.
/// </remarks>
internal class DispatcherScheduler : LocalScheduler, ISchedulerPeriodic
{

    /// <summary>
    /// Constructs a <see cref="System.Reactive.Concurrency.DispatcherScheduler"/> that schedules units of work on the given <see cref="System.Windows.Threading.Dispatcher"/>.
    /// </summary>
    /// <param name="dispatcher"><see cref="System.Reactive.Concurrency.DispatcherScheduler"/> to schedule work on.</param>
    /// <exception cref="ArgumentNullException"><paramref name="dispatcher"/> is <c>null</c>.</exception>
    public DispatcherScheduler(System.Windows.Threading.Dispatcher dispatcher)
    {
        Dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
        Priority = System.Windows.Threading.DispatcherPriority.Normal;

    }

    /// <summary>
    /// Constructs a <see cref="System.Reactive.Concurrency.DispatcherScheduler"/> that schedules units of work on the given <see cref="System.Windows.Threading.Dispatcher"/> at the given priority.
    /// </summary>
    /// <param name="dispatcher"><see cref="System.Reactive.Concurrency.DispatcherScheduler"/> to schedule work on.</param>
    /// <param name="priority">Priority at which units of work are scheduled.</param>
    /// <exception cref="ArgumentNullException"><paramref name="dispatcher"/> is <c>null</c>.</exception>
    public DispatcherScheduler(System.Windows.Threading.Dispatcher dispatcher, System.Windows.Threading.DispatcherPriority priority)
    {
        Dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
        Priority = priority;
    }

    /// <summary>
    /// Gets the <see cref="System.Windows.Threading.Dispatcher"/> associated with the <see cref="System.Reactive.Concurrency.DispatcherScheduler"/>.
    /// </summary>
    public System.Windows.Threading.Dispatcher Dispatcher { get; }

    /// <summary>
    /// Gets the priority at which work items will be dispatched.
    /// </summary>
    public System.Windows.Threading.DispatcherPriority Priority { get; }

    /// <summary>
    /// Schedules an action to be executed on the dispatcher.
    /// </summary>
    /// <typeparam name="TState">The type of the state passed to the scheduled action.</typeparam>
    /// <param name="state">State passed to the action to be executed.</param>
    /// <param name="action">Action to be executed.</param>
    /// <returns>The disposable object used to cancel the scheduled action (best effort).</returns>
    /// <exception cref="ArgumentNullException"><paramref name="action"/> is <c>null</c>.</exception>
    public override IDisposable Schedule<TState>(TState state, Func<IScheduler, TState, IDisposable> action)
    {
        if (action == null)
        {
            throw new ArgumentNullException(nameof(action));
        }

        var d = new SingleAssignmentDisposable();

        Dispatcher.BeginInvoke(
                               new Action(() =>
                               {
                                   if (!d.IsDisposed)
                                   {
                                       d.Disposable = action(this, state);
                                   }
                               }),
                               Priority
                              );

        return d;
    }

    /// <summary>
    /// Schedules an action to be executed after <paramref name="dueTime"/> on the dispatcher, using a <see cref="System.Windows.Threading.DispatcherTimer"/> object.
    /// </summary>
    /// <typeparam name="TState">The type of the state passed to the scheduled action.</typeparam>
    /// <param name="state">State passed to the action to be executed.</param>
    /// <param name="action">Action to be executed.</param>
    /// <param name="dueTime">Relative time after which to execute the action.</param>
    /// <returns>The disposable object used to cancel the scheduled action (best effort).</returns>
    /// <exception cref="ArgumentNullException"><paramref name="action"/> is <c>null</c>.</exception>
    public override IDisposable Schedule<TState>(TState state, TimeSpan dueTime, Func<IScheduler, TState, IDisposable> action)
    {
        if (action == null)
        {
            throw new ArgumentNullException(nameof(action));
        }

        var dt = Scheduler.Normalize(dueTime);
        if (dt.Ticks == 0)
        {
            return Schedule(state, action);
        }

        return ScheduleSlow(state, dt, action);
    }

    private IDisposable ScheduleSlow<TState>(TState state, TimeSpan dueTime, Func<IScheduler, TState, IDisposable> action)
    {
        var d = new MultipleAssignmentDisposable();

        var timer = new System.Windows.Threading.DispatcherTimer(Priority, Dispatcher);

        timer.Tick += (s, e) =>
        {
            var t = Interlocked.Exchange(ref timer, null);
            if (t != null)
            {
                try
                {
                    d.Disposable = action(this, state);
                }
                finally
                {
                    t.Stop();
                    action = static (s, t) => Disposable.Empty;
                }
            }
        };

        timer.Interval = dueTime;
        timer.Start();

        d.Disposable = Disposable.Create(() =>
        {
            var t = Interlocked.Exchange(ref timer, null);
            if (t != null)
            {
                t.Stop();
                action = static (s, t) => Disposable.Empty;
            }
        });

        return d;
    }

    /// <summary>
    /// Schedules a periodic piece of work on the dispatcher, using a <see cref="System.Windows.Threading.DispatcherTimer"/> object.
    /// </summary>
    /// <typeparam name="TState">The type of the state passed to the scheduled action.</typeparam>
    /// <param name="state">Initial state passed to the action upon the first iteration.</param>
    /// <param name="period">Period for running the work periodically.</param>
    /// <param name="action">Action to be executed, potentially updating the state.</param>
    /// <returns>The disposable object used to cancel the scheduled recurring action (best effort).</returns>
    /// <exception cref="ArgumentNullException"><paramref name="action"/> is <c>null</c>.</exception>
    /// <exception cref="ArgumentOutOfRangeException"><paramref name="period"/> is less than <see cref="TimeSpan.Zero"/>.</exception>
    public IDisposable SchedulePeriodic<TState>(TState state, TimeSpan period, Func<TState, TState> action)
    {
        if (period < TimeSpan.Zero)
        {
            throw new ArgumentOutOfRangeException(nameof(period));
        }

        if (action == null)
        {
            throw new ArgumentNullException(nameof(action));
        }

        var timer = new System.Windows.Threading.DispatcherTimer(Priority, Dispatcher);

        var state1 = state;

        timer.Tick += (s, e) =>
        {
            state1 = action(state1);
        };

        timer.Interval = period;
        timer.Start();

        return Disposable.Create(() =>
        {
            var t = Interlocked.Exchange(ref timer, null);
            if (t != null)
            {
                t.Stop();
                action = static _ => _;
            }
        });
    }
}